The use of telescoping bodies which have nested elements to make an object more compact is well known, and has been practiced for a long time. One of the problems presented by any sort of telescoping body using nested elements is in controlling movement of the elements relative to one another. This can be a particularly vexing problem when the telescoping body is load-bearing, such as the support member for a music stand.
In a music stand there is typically a support member comprised of an outer tube, and an inner tube which is slidably mounted within the outer tube. This support member is vertically oriented, with the music holder mounted on top of the upper end of the inner tube. The weight of the music holder and any music placed on the music holder presents a problem, given the telescopic nature of the music stand. It is important that the height of the music stand be easily adjustable, but it is equally important that the adjustment be retained and that the inner tube of the music stand remain stationary relative to the outer tube of the music stand when adjustments are completed and the stand is in use.
Attempts to achieve the desired adjustment with music stands is illustrative of attempts to achieve adjustments with telescoping bodies in general. The simplest and most straight forward way of achieving this adjustment is to crimp the upper end of the outer tube against the inner tube body, using the friction from the outer tube upper end to hold the inner tube stationary, while allowing it to be adjustable. This method has a number of limitations, including the fact that it requires a very precise fit with the inner and outer tubes, especially at the crimp of the outer tube upper end. As the stand is repeatedly used, excessive wear to both the inner tube body and the crimped outer tube upper end causes the stand to fail to hold its adjustment.
Another mechanism used to adjust music stands is one which adds a threaded collar to the outer tube and causes the tightening of some portion of the outer tube upper end, or a contained gasket or "O" ring, against the inner tube body, thereby holding it in place once the adjustment is made. This mechanism and its production adds costs to the music stand, and is less convenient to use when adjusting the music stand, requiring the loosening and tightening of the threaded cap. Also, if the mechanism uses gaskets they can be worn and have to be replaced.
Several adjustment mechanisms have been tried using a spring mounted internally in the overlapping space between the inner and outer tubes. While these mechanisms represent some difficulty in increased cost in manufacturing, some success has been achieved. One mechanism that achieved a great deal of success was a clutch device which used a plurality of fingers arranged substantially uniformly about the inner tube proximate the inner tube lower end. These fingers were held in place by a collar which fit around the inner tube lower end and has one end of each of the fingers held between it and the inner tube. The fingers themselves were bowed outward from the inner tube so they are pressed against the outer tube. This adjustment mechanism allows the inner tube to be moved up and down by simply grasping the upper end of the inner tube or a music desk attached to the upper end of the inner tube and lifting up or pushing down. At the same time the plurality of fingers constituting the clutch provided sufficient friction to prevent the inner tube from sliding downward even when the music was on the music desk.
The above described mechanism, however, was relatively expensive to produce in that its production was relatively labor intensive. Individual fingers had to be produced and then manually inserted into the jig which held them in their arrayed position. The inner tube lower end was placed in the middle of fingers then pressed down so that it was inserted between the fingers lower end and the outer collar. Thus, this mechanism required separate production of fingers and collars and further assembly by hand, which made it relatively expensive to produce. At the same time, it proved to be a generally superior mechanism for achieving the desired combination of ease of adjustment and ability to hold the adjustment once the desired adjustment was achieved.
As illustrated by the above discussion, there are a number of desirable features for a shaft clutch mechanism and method for its production. It would be desirable for a shaft clutch mechanism to allow easy adjustment of a telescopic body utilizing nested elements, and at the same time allowing the adjustment to be retained once achieved. It also would be desirable for a shaft clutch mechanism to have a plurality of fingers arrayed about an inner nested element of a telescopic body. It further would be desirable to have a shaft clutch mechanism which had a plurality of fingers arrayed about an inner nested body with the shaft clutch mechanism being constructed from a single piece of material. Additionally, it would be desirable to have a shaft clutch mechanism produced by a fully or partially automated method and apparatus.
While the discussion herein relates to shaft clutch mechanisms for telescoping bodies such as music stands, and methods and apparatuses for their production, it is not intended that the invention be limited to this situation. It will be obvious from the description that follows that the present invention will be useful in other applications with problems common to those described herein.